As a hobby, smoking attracts many persons, especially men. However, tar of cigarettes comprises dozens of kinds of carcinogenic ingredients and is harmful to human bodies. Furthermore, second-hand smoking does great harm to non-smokers. Therefore, most public places have bans on smoking. But it is difficult to stop smoking for a smoker. Thus, electronic cigarettes have been more and more widely used as a substitute for traditional tobacco.
An electronic cigarette is provided with a cigarette-holder. When a switch of the electronic cigarette is turned on, the electronic cigarette can be smoked via the cigarette-holder or an airflow sensor. The electronic cigarette can be put back into a cigarette box for the next use after it is smoked. However, a typical electronic cigarette that has not been smoked is not different from such an electronic cigarette that has been smoked, and thus it is difficult to determine whether such an electronic cigarette has been smoked or not. When a plurality of persons smoke electronic cigarettes stored in a same cigarette box, one of the electronic cigarettes may be shared by different users, which may adversely affect the users' health and become a transmission way of many diseases.